Please do not second guess yourself because of his actions. You made your decision to separate, for a reason. And it took a lot of courage to do so. I know first hand, that checking up on them sets you back. You are either going to see something that will be damaging and could potentially put you over the edge, or you could see what you did see...or hear...a glimpse of hope. Either way, it affects your ability to heal and get on with your life. Checking up, in my opinion, can easily put you back to square one like what you are going through...and it is torture.
I know that it is extremely hard because I feel and have read, we do get addicted to our addicted loved ones. It will take time to get it out of your system. I feel for you, I really, really do. But you are a strong person. Look at the progress you've made by taking the steps that you did!! I commend you for saying "enough" and deciding that YOUR life and happiness are important. You can do this!!! We are here to support you!